The present invention relates to a process for chemically modifying food materials, and the products formed thereby. More particularly, this invention relates to a process for hydroxypropylating starch and said hydroxypropylated starch. Specifically, this invention produces a hydroxypropylated starch with no detectable residue of prpopylene chlorohydrin.
Etherification of starch improves many of the starch's characteristics. U.S. Pat. No. 2,516,634 issued to Kesler et al. describes the use of a starch etherification process to produce a coldwater swelling starch. Additionally, hydroxypropylation of starch improves the physical characteristics related to the starch's performance as a thickener in products such as puddings. Further advantages of hydroxypropylation include: lowering the gelatinization temperature; increasing the water binding capacity; increasing the starch's lipophilic compatibility, and decreasing the starches tendency toward retrogradation.
Traditionally, the production of hydroxypropylated starch ignores the formation of side products. The addition of starch to an aqueous, alkali, hydroxypropylation-catalyst-containing solution is the first step in the traditional procedure. Once the slurry is homogeneous, propylene oxide is added. After sufficient hydroxypropylation of the starch, the starch may be neutralized and dried, or the starch may be crosslinked, and thereafter neutralized and dried.
Nevertheless, the starch art needs a new hydroxypropylation method. The classical procedure produces propylene chlorohydrin as a side product which remains in the hydroxypropylated starch. However, Governmental regulatory bodies are considering stricter regulation of the chlorohydrin level permissable in foodstuffs. While the chlorohydrin presence can be reduced to an acceptable level by extensive washing, this washing produces significant starch losses.